Re: Flyback Troubleshooting help

Does your generator have a knob marked "DC offset"? If so, set it for a -4
to +4 volt square wave. Using 0 to +8 volts isn't going to give you useful
readings.

On Mon, Jan 17, 2011 at 2:19 PM, Jess Askey <jess@askey.org> wrote:

> Okay, I put the standalone LOPT onto my square wave generator
> (unfortunately my generator can only supply 30ma) so Im not sure that is
> enough.
>
> Here is the signal before attaching the LOPT.... 15KHz 9vP-P
>
>
> http://gamearchive.askey.org/Video_Games/Manufacturers/Atari/monitors/amplifone/raster/images/generator_output_15k.jpg
>
> Here is the primary with that signal attached... secondaries are exactly
> the same waveform, yet in different ratios (and those ratios are not
> correct)
>
>
> http://gamearchive.askey.org/Video_Games/Manufacturers/Atari/monitors/amplifone/raster/images/lopt_ringing_15k.jpg
>
> Doesn't look right.
>
> When I read a DC voltage on the Anode cap, I have 2.2VDC, pretty low. :-(
>
>
>
>
> On 1/17/2011 12:36 PM, John Robertson wrote:
>
>> Jess Askey wrote:
>>
>>> From what I read, I figure that if there was a short the Q would be
>>> lowered enough that I wouldn't get any ringing... even in circuit. However,
>>> with that said, since my ringing is drastically *lower* than I expect (I
>>> thought there should be a 300V oscillation on the collector with a 36V
>>> supply), something is dragging this down.... so I think it is simply ringing
>>> at the expense of excessive current because the Q *is* lower.
>>>
>>> I will try the low voltage out of circuit ring test today and report
>>> back... with the low amounts of current, Im guessing that I will not get a
>>> *good* ring out of it.
>>>
>>> jess
>>>
>>>
>>> On 1/17/2011 12:56 AM, Rodger Boots wrote:
>>>
>>>>
>>>> John, it's a raster monitor, not vector.
>>>>
>>>> So why is it ringing in the first place? Is the damper diode connected?
>>>> Is the horizonal output transistor the correct part? Is the correct yoke
>>>> winding connected? Is the filter capacitor on the power supply to the
>>>> output transformer working (should be DC to the transformer, very little
>>>> AC).
>>>>
>>>> ---------
>>>
>>
>>
>> Have you checked your input bridge yet (4x 1N4004) as well as the 12V
>> regulator U4(78L12) (not too likely, but if shorted then Q7 is also bad) for
>> damage from the un-isolated 120VAC power test you did? PTC1 should be fine -
>> no connection to ground there. Pg 54 of schematic PDF.
>>
>> I would separate the flyback from the circuit and then hook up pins 1
>> (common) and 4 (pulsing DC) to some AC supply using a bridge rectifier to
>> get pulsing DC running at the correct frequency (otherwise the transformer
>> is not efficient - results will be skewed lower). Hook a scope up to pins 1
>> & 4 to see the picture, it should be fairly clean.
>>
>> Then scope pin 5 to see if you have a bit of a boost on the pulsing DC,
>> next scope across pins 7 (probe) & 9 (common) should show AC about 15-20% of
>> the original input voltage (120/24), pins 6 & 9 showing around 5% (filament
>> of 6.3VAC). You can also use a HV probe (if you have one) for the HV output,
>> again it should be the ratio of your test voltage to 120V.
>>
>> John :-#)#
>>
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Received on Mon Jan 17 16:16:51 2011